I'm not an ageist but running a 73 year old candidate for Senate just doesn't sit well with me. He'd probably be one of the oldest freshman Senators ever.
Ed Markey was like 68 when he was elected in 2013. Strickland is in great health, too.
Ignoring seat warmers, the winner is 78 year-old Frank Lautenberg. He was already a Senator, but had previously retired.
As for current Senators, Agnus King and Dan Coats (previous Senator) were slightly older than Ed Markey.
Strom Thurmond managed to be a 100 year-old Senator, and actually retired rather than dying in office.
